The present invention relates to a voice coil driving auto-focus lens module, especially to a lens module in which an optical lens is driven to move forward and backward for auto-focusing by spring force of spring set as well as electromagnetic force.
The digital cameras or mobile phones with shooting function are disposed with a lens module that drives optical lenses to move along an optical axis for autofocus or zoom. One of the driving mechanisms of the optical lens is voice coil motor (VCM). By applying a current to the coil to generate an electromagnetic field, a driving force is generated by the electromagnetic field and a permanent magnet so as to drive the optical lens. Such design can minimize volume of the lens module so that the VCM has been applied to small-size cameras, camera-equipped cellular phones or web-cameras broadly.
A conventional VCM-type autofocus lens module is shown in FIG. 1, as those disclosed in US2008/0013196, U.S. Pat. No. 6,594,450, U.S. Pat. No. 7,145,738, TWM317027, JP3124292, and JP3132575. The VCM-type autofocus lens module mainly includes a bottom cover 110, two conductive plates 122, an insulation spacer 130, four permanent magnets 140, a lens holder 150, an optical lens 160, a coiled spring 171, a coil 180, and a top cover 190. A lens set moving along the optical axis is formed by the lens holder 150, the optical lens 160, and the coil 180. While the coiled spring 171 being used, the coiled spring 171 generates an elastic fore directly and effectively so as to make the lens holder 150 move fast. Yet the lens module may be tilted during the movement so that the requirement of high precision is unable to achieve. Refer to FIG. 2, alternative VCM-type autofocus lens module is disclosed. The lens holder 150 is moved by an elastic force of a leaf spring 172, as prior arts revealed in US2008/0186601, US2006/0181632, TWM331687, TWM318736, and JP63247924. But both the elasticity and extension length of the leaf spring 172 are not so strong so that the movement of the lens module is slower and the requirement of quick focusing is unable to be matched. In some prior arts, even two leaf springs 172 are used so as to overcome the problem of insufficient extension length but the slow movement is still a problem.
Thus there is a need to invent a new design of the lens module without too much modification of the design available now that satisfies the requirements of high precision, quick-focusing and reduced tilt by elasticity force of spring set.